The performance of voltage regulators of various types (e.g. switched-mode voltage converters such as buck converters or linear voltage regulators such as Low Drop Out, LDO, voltage regulators) subject to load transients is typically tested during the design phase of the voltage regulators. Such load transient tests may be performed using an open loop test device which comprises a switching element in series with a current limiting resistor. The test device is coupled to the output of the voltage regulator. The switching element of the test device may be used to turn on/off the load, thereby submitting the voltage regulator to the load transient (no load, i.e. no load current, if the switch is turned off and a pre-determined load, i.e. a pre-determined load current through the resistor, if the switch is turned on). Usually an excitation circuit drives the switching element (e.g. a transistor) to saturation when turning on the switch, such that the current limiting resistor appears as a load to the voltage regulator.
The use of the above mentioned open loop test device for testing the performance of a voltage regulator subject to load transients has various disadvantages. In particular, the open loop test device does not provide any possibility to control the rise and/or fall edges of the load transient. Furthermore, the open loop test device does not provide any possibility to control the initial load current of the load transient. In addition, the open loop test device does not provide any possibility to control the amplitude of the load current because a fixed limiting resistor is used.
This requires a change of the current limiting resistor when a different output voltage of the voltage regulator is to be tested.
The present document addresses the above mentioned shortcomings of load transient test devices. In particular, the present document describes a test device which allows for a relatively high current sink (i.e. for a relatively high load current) even while operating the voltage regulator under test with low output voltages. In addition, the test device allows to control the rise and/or fall edges of the load transient, to control the amplitude of the load current, and/or to control a steady state current offset. Furthermore, the test device allows for fast slew rates, e.g. of more than 50 A/μs at 1V of regulator output voltage.